The objective of this study was to summarize and critically assess the effects of interventions to prevent HIV/AIDS among adolescents in less developed countries. Reports of studies that evaluated interventions for preventing HIV/AIDS/STDs among persons aged 11-25 years were obtained from online computer databases, by searching conference proceedings and relevant journals, and by following up references cited in published reports. Studies were included if they investigated any educational, behavioral, psychosocial or other intervention that aimed to prevent or reduce HIV/AIDS/STD among persons aged 11-25 years in a less developed country. Only studies that included a control group, and which involved pre- and post-intervention assessments were included. Outcome measures included: (i) changes in safe sex practices (abstinence, condom use, limitation of sexual partners, avoidance of casual sex), (ii) knowledge about HIV/AIDS transmission and prevention methods, (iii) perception of HIV/AIDS/STD risks, (iv) self-efficacy with regard to condom negotiation and refusal of sex, (v) uptake of voluntary counseling and testing (VCT), and (vi) reduction in incidence of HIV/AIDS/STDs. Studies were assessed in terms of intervention format (e.g., education, role-play, video), duration, and setting (school or community). Reported improvements in outcome measures in intervention versus control groups were assessed. Sixteen studies met the inclusion criteria. Thirteen of these were conducted in Africa and three in Latin America. Twelve of the sixteen studies were school-based, and four were community-based. The interventions reviewed were not resoundingly successful in achieving their goals of increasing knowledge of HIV/AIDS, altering attitudes, improving negotiation and communication skills, or in influencing positive behavior evidenced through consistent condom use, abstinence, or reducing the number of partners. Considering the importance of HIV/AIDS prevention among adolescents, design of evaluation studies of programs in less developed countries need to be improved. The use of randomized controlled trials or other rigorous approaches for evaluating population-based behavioral interventions (e.g., Solomon Four design) is recommended. © Freund Publishing House Ltd.